Investigating Substrate Loss in MEMS Acoustic Resonators and On-Chip Inductors.

This work studies the influence of substrate loss on the performance of acoustic resonators and on-chip inductors and investigates the effective substrate resistivity of seven commonly used substrates in silicon-based devices. The substrates include X-cut lithium niobate (LiNbO3) film with two different thicknesses (400 nm and 1.6 [Formula: see text]) on high-resistivity Si (HR-Si) and amorphous Si wafers, SiO2 film with two different thicknesses on HR-Si, and bare HR-Si. The effective resistivities of these substrates are extracted using coplanar waveguides (CPWs) over a frequency range from 1 to 40 GHz. Using the effective resistivity approach, the efficiency of two substrate loss reduction techniques-Si wafer removal and amorphous Si-in reducing substrate loss is quantified. Comparison of the extracted substrate resistivities of the suspended and un-suspended dielectric-on-Si structures and comparison of LiNbO3 on HR-Si and amorphous Si are carried out. Substrate loss reduction techniques are more advantageous for a thinner dielectric film and at a lower frequency range due to the higher filling factor of the electric field in the Si wafer. Finally, by comparison of the effective substrate resistivity of SiO2 film on an HR-Si with bare HR-Si, thick plasma-enhanced chemical vapor deposition (PECVD) SiO2 film is found to be a good insulation layer to reduce substrate loss.

Lateral Spurious Mode Suppression in Lithium Niobate A1 Resonators.

This work presents an improved design that exploits dispersion matching to suppress the spurious modes in the lithium niobate first-order antisymmetric (A1) Lamb wave mode resonators. The dispersion matching in this work is achieved by micro-machining the lithium niobate thin film to balance the electrical and mechanical loadings of electrodes. In this article, the dispersion matchings of the A1 mode in lithium niobate based on different metals are analytically modeled and validated with finite-element analysis. The fabricated devices exhibit spurious-free responses with a quality factor of 692 and an electromechanical coupling coefficient of 28%. The demonstrated method herein could overcome a significant hurdle that is currently impeding the commercialization of A1 devices.

Wideband Hybrid Monolithic Lithium Niobate Acoustic Filter in the K-Band.

This article presents the design approach and the first demonstration of a wideband hybrid monolithic acoustic filter in the K -band, which exceeds the limitation of electromechanical coupling on the fractional bandwidth (FBW) of acoustic filters. The hybrid filter utilizes the codesign of electromagnetic (EM) and acoustic to attain wide bandwidth while keeping the advantages of small sizes and high Q in the acoustic domain. The performance trade space and design flow of the hybrid filter are also presented in this article, which allows this technology to be applied for filters with different center frequencies and FBWs. The hybrid filter is simulated by hybridizing the EM and acoustic finite element analysis, which are carried out separately and combined at a system level. The fabricated filter built with resonators having an electromechanical coupling of 0.7% based on the seventh-order antisymmetric Lamb wave mode (A7) has a 3-dB FBW of 2.4% at 19 GHz and a compact footprint of 1.4 mm2.

A Frequency Independent Framework for Synthesis of Programmable Non-reciprocal Networks.

Passive and linear nonreciprocal networks at microwave frequencies hold great promises in enabling new front-end architectures for wireless communication systems. Their non-reciprocity has been achieved by disrupting the time-reversal symmetry using various forms of biasing schemes, but only over a limited frequency range. Here we demonstrate a framework for synthesizing theoretically frequency-independent multi-port nonreciprocal networks. The framework is highly expandable and can have an arbitrary number of ports while simultaneously sustaining balanced performance and providing unprecedented programmability of non-reciprocity. A 4-port circulator based on such a framework is implemented and tested to produce a broadband nonreciprocal performance from 10 MHz to 900 MHz with a temporal switching effort at 23.8 MHz. With the combination of broad bandwidth, low temporal effort, and high programmability, the framework could inspire new ways of implementing multiple input multiple output (MIMO) communication systems for 5G.